I hear what you're saying, but tell that to Apple when they see Samsung phones
To be sure, hard work and constant training is what yields results in any martial art - but people can certainly take and incorporate others methods, and those methods are what you train and put hard work into.
But I don't disagree with you - these days if people teach openly (publicly) they shouldn't be worried about sharing with video, online posts, offering open seminars, etc. If someone really is that protective then they shouldn't be teaching publicly, just train in secret with family (and hope they have no black sheep in the family).